Chapter 16: Digestion and Absorption – Short Answer Type Questions
CBSE Class 11 Biology Chapter 16 – Digestion and Absorption | Short Answer Type Questions (NCERT)
Course & Examination Details
Course: CBSE Class 11 Biology
Unit: Unit V – Human Physiology
Chapter: Chapter 16 – Digestion and Absorption
Board: Central Board of Secondary Education (CBSE)
Question Type: Short Answer Type Questions
Answer Length: 60–80 words
Syllabus: Strictly as per NCERT Biology Textbook
Section A: Human Digestive System (Q1–Q18)
Q1. Define digestion and explain its significance.
Answer:
Digestion is the process by which complex food substances are broken down into simpler, soluble forms that can be absorbed by the body. It is essential because large food molecules like proteins, starch, and fats cannot be directly absorbed. Digestion converts them into amino acids, sugars, fatty acids, and glycerol, which are used for energy production, growth, tissue repair, and maintenance of body functions.
Q2. Describe the components of the human digestive system.
Answer:
The human digestive system consists of the alimentary canal and associated digestive glands. The alimentary canal extends from the mouth to the anus and includes the mouth, pharynx, oesophagus, stomach, small intestine, and large intestine. Digestive glands include salivary glands, liver, and pancreas. Together, they help in digestion, absorption, assimilation, and egestion of food.
Q3. Explain the role of the buccal cavity in digestion.
Answer:
The buccal cavity plays an important role in both mechanical and chemical digestion. Teeth grind food into smaller particles, increasing surface area for enzyme action. Saliva secreted by salivary glands moistens food and contains salivary amylase, which initiates digestion of starch into maltose. The tongue helps in mixing food with saliva and swallowing.
Q4. What is the dental formula of adult humans and what does it indicate?
Answer:
The dental formula of adult humans is 2123 / 2123. It indicates the number and arrangement of different types of teeth in each half of the upper and lower jaws. This means humans have two incisors, one canine, two premolars, and three molars on each side, showing heterodont dentition adapted for varied food habits.
Q5. Describe the function of saliva in digestion.
Answer:
Saliva moistens food, making it easier to swallow. It contains salivary amylase, which begins the digestion of starch by converting it into maltose. Saliva also contains mucus that lubricates food and helps protect the oral cavity. The slightly alkaline nature of saliva provides a suitable medium for enzyme activity.
Q6. Explain peristalsis and its importance.
Answer:
Peristalsis is the rhythmic contraction and relaxation of circular and longitudinal muscles of the alimentary canal. It helps in the movement of food from the oesophagus to the stomach and through the intestines. Peristalsis ensures continuous movement of food irrespective of body position and plays a vital role in digestion and absorption.
Q7. Describe the structure and function of the stomach.
Answer:
The stomach is a J-shaped muscular organ divided into cardiac, fundic, and pyloric regions. It stores food temporarily, churns it mechanically, and mixes it with gastric juice. Gastric glands secrete hydrochloric acid, pepsinogen, mucus, and rennin in infants. The stomach partially digests proteins and converts food into semi-liquid chyme.
Q8. What is the role of hydrochloric acid in the stomach?
Answer:
Hydrochloric acid creates an acidic environment in the stomach, which is essential for the activation of pepsinogen into pepsin. It also helps in killing harmful microorganisms present in food. Additionally, HCl facilitates protein digestion by denaturing proteins, making them more accessible to enzymatic action.
Q9. Explain the importance of mucus in gastric juice.
Answer:
Mucus secreted by gastric glands forms a protective layer over the stomach lining. It prevents damage to the stomach wall from the corrosive action of hydrochloric acid and digestive enzymes like pepsin. This protection is essential to prevent ulcers and maintain the integrity of the stomach lining during digestion.
Q10. Why is the small intestine called the main site of digestion?
Answer:
The small intestine is called the main site of digestion because most chemical digestion of carbohydrates, proteins, fats, and nucleic acids occurs here. Pancreatic juice, bile, and intestinal juice act together to complete digestion. The alkaline medium and presence of numerous enzymes make digestion highly efficient in the small intestine.
Q11. Name the parts of the small intestine and state one function of each.
Answer:
The small intestine consists of three parts: duodenum, jejunum, and ileum. The duodenum receives bile and pancreatic juice for digestion. The jejunum is mainly involved in digestion and absorption of nutrients. The ileum absorbs digested nutrients into blood and lymph through villi and microvilli.
Q12. Describe the structure and function of the large intestine.
Answer:
The large intestine consists of caecum, colon, and rectum. It absorbs water and electrolytes from undigested food, helping in formation of faeces. Beneficial bacteria in the colon produce certain vitamins. The rectum temporarily stores faeces before elimination through the anus during defecation.
Q13. Explain the function of the liver in digestion.
Answer:
The liver produces bile, which is essential for fat digestion. Bile salts emulsify large fat globules into smaller droplets, increasing surface area for lipase action. The liver also plays a role in detoxification, metabolism of nutrients, and storage of glycogen, although bile itself does not contain digestive enzymes.
Q14. What is the role of the gall bladder?
Answer:
The gall bladder stores and concentrates bile produced by the liver. When food enters the duodenum, bile is released into the small intestine through the bile duct. This helps in emulsification and digestion of fats, making the process more efficient.
Q15. Describe the digestive role of the pancreas.
Answer:
The pancreas secretes pancreatic juice, which contains enzymes such as amylase, trypsinogen, chymotrypsinogen, lipase, and nucleases. These enzymes digest carbohydrates, proteins, fats, and nucleic acids in the small intestine. Pancreatic juice also provides an alkaline medium necessary for enzyme action.
Q16. What is chyme and where is it formed?
Answer:
Chyme is a semi-fluid, acidic mixture of partially digested food formed in the stomach. It results from the mechanical churning of food and mixing with gastric juice. Chyme passes gradually into the duodenum for further digestion.
Q17. What is egestion and how does it differ from excretion?
Answer:
Egestion is the elimination of undigested and unabsorbed food through the anus. Excretion, on the other hand, is the removal of metabolic wastes produced by body cells. Egestion removes digestive waste, whereas excretion removes cellular waste products like urea.
Q18. Explain the significance of the alimentary canal being muscular.
Answer:
The muscular nature of the alimentary canal allows movements like peristalsis and segmentation. These movements mix food with digestive juices and propel it forward. Muscular contractions ensure proper digestion, absorption, and transport of food through different parts of the digestive system.
Section B: Digestive Enzymes (Q19–Q35)
Q19. Describe digestion of carbohydrates in humans.
Answer:
Carbohydrate digestion begins in the mouth where salivary amylase converts starch into maltose. In the small intestine, pancreatic amylase continues starch digestion. Intestinal enzymes like maltase, sucrase, and lactase convert disaccharides into monosaccharides such as glucose, fructose, and galactose, which are readily absorbed.
Q20. Explain digestion of proteins in the stomach.
Answer:
Protein digestion in the stomach begins with the action of pepsin. Pepsinogen secreted by gastric glands is activated into pepsin by hydrochloric acid. Pepsin breaks proteins into proteoses and peptones. The acidic environment of the stomach is essential for pepsin activity.
Q21. How does protein digestion continue in the small intestine?
Answer:
In the small intestine, pancreatic enzymes like trypsin and chymotrypsin further break down proteins and peptides. Intestinal peptidases then convert peptides into amino acids. These amino acids are the final products of protein digestion and are absorbed through the intestinal lining.
Q22. Explain the digestion of fats in humans.
Answer:
Fat digestion occurs in the small intestine. Bile salts emulsify fats into small droplets, increasing surface area. Pancreatic lipase then breaks fats into fatty acids and glycerol. Fat digestion requires an alkaline medium and is completed in the intestine.
Q23. What is emulsification of fats and why is it important?
Answer:
Emulsification is the process of breaking large fat globules into smaller droplets by bile salts. It increases the surface area of fats, allowing pancreatic lipase to act more efficiently. Without emulsification, fat digestion would be slow and incomplete.
Q24. Describe digestion of nucleic acids.
Answer:
Nucleic acids are digested in the small intestine by pancreatic nucleases, which convert them into nucleotides. Intestinal enzymes further break nucleotides into sugars, nitrogenous bases, and phosphates, which are then absorbed into the bloodstream.
Q25. Why does bile not contain digestive enzymes?
Answer:
Bile does not contain digestive enzymes because its primary function is emulsification of fats. It provides bile salts that increase surface area for enzyme action and helps neutralize acidic chyme, creating an alkaline medium for pancreatic enzymes.
Q26. Explain the role of intestinal juice.
Answer:
Intestinal juice contains enzymes like maltase, sucrase, lactase, peptidases, and lipase. These enzymes complete the digestion of carbohydrates, proteins, and fats into absorbable forms. Intestinal juice ensures final digestion at the brush border of intestinal cells.
Q27. What activates trypsinogen and why is this important?
Answer:
Trypsinogen is activated into trypsin by the enzyme enterokinase present in the intestinal mucosa. This activation is important because trypsin then activates other proteolytic enzymes, ensuring efficient protein digestion while preventing damage to pancreatic tissues.
Q28. Why does digestion of fats not occur in the stomach?
Answer:
Fat digestion does not occur in the stomach because lipase works effectively only in an alkaline medium. The stomach is acidic, which inhibits fat digestion. Major fat digestion occurs in the small intestine after emulsification by bile.
Q29. Name the enzymes responsible for digestion of disaccharides.
Answer:
Maltase digests maltose into glucose, sucrase digests sucrose into glucose and fructose, and lactase digests lactose into glucose and galactose. These enzymes are present in intestinal juice.
Q30. How is lactose intolerance related to digestion?
Answer:
Lactose intolerance occurs due to deficiency of lactase enzyme. As a result, lactose is not digested properly, leading to symptoms like bloating, diarrhoea, and abdominal pain when dairy products are consumed.
Q31. What is the role of pancreatic amylase?
Answer:
Pancreatic amylase continues the digestion of starch in the small intestine by converting it into maltose and dextrins. It acts in an alkaline medium provided by pancreatic juice and bile.
Q32. Why is the digestion of proteins incomplete in the stomach?
Answer:
Protein digestion in the stomach is incomplete because pepsin only breaks proteins into proteoses and peptones. Complete digestion into amino acids requires pancreatic and intestinal enzymes present in the small intestine.
Q33. What is the importance of alkaline medium in the intestine?
Answer:
An alkaline medium in the small intestine neutralizes acidic chyme and provides optimal conditions for pancreatic and intestinal enzymes. Enzymes like trypsin, lipase, and amylase function efficiently only in alkaline conditions.
Q34. Explain the role of rennin in infants.
Answer:
Rennin is secreted in the stomach of infants. It helps in digestion of milk proteins by converting milk casein into paracasein, which is then acted upon by pepsin. Rennin is absent in adults.
Q35. Why are digestive enzymes substrate-specific?
Answer:
Digestive enzymes are substrate-specific because their active sites are complementary to specific substrates. This ensures precise and efficient digestion of carbohydrates, proteins, and fats without affecting other molecules.
Section C: Absorption Process (Q36–Q50)
Q36. Define absorption and mention its importance.
Answer:
Absorption is the process by which digested nutrients pass through the intestinal mucosa into blood or lymph. It is important because only absorbed nutrients can be transported to body cells for energy production, growth, and repair.
Q37. Describe the structural adaptations of the small intestine for absorption.
Answer:
The small intestine has villi and microvilli that greatly increase surface area. Each villus contains blood capillaries and a lacteal for transport of nutrients. Thin epithelial lining facilitates rapid absorption of digested food.
Q38. Explain absorption of carbohydrates.
Answer:
Carbohydrates are absorbed as monosaccharides like glucose, fructose, and galactose. Glucose and galactose are absorbed by active transport, while fructose is absorbed by facilitated diffusion into blood capillaries.
Q39. How are amino acids absorbed?
Answer:
Amino acids are absorbed mainly by active transport across the intestinal epithelium. They enter blood capillaries in the villi and are transported to the liver through the hepatic portal vein.
Q40. Describe absorption of fats.
Answer:
Fatty acids and glycerol form micelles and diffuse into intestinal cells. Inside the cells, they are re-synthesized into fats and packed as chylomicrons, which enter the lacteals and are transported through lymph.
Q41. What are chylomicrons?
Answer:
Chylomicrons are lipoprotein particles formed in intestinal cells. They transport absorbed fats through the lymphatic system before entering the bloodstream.
Q42. How are vitamins absorbed?
Answer:
Water-soluble vitamins are absorbed by diffusion or active transport into blood. Fat-soluble vitamins A, D, E, and K are absorbed along with fats through lymph as chylomicrons.
Q43. Explain absorption of minerals.
Answer:
Minerals are absorbed by passive diffusion or active transport depending on their concentration and body requirements. Calcium, iron, and sodium often require active transport mechanisms.
Q44. Which substances are absorbed in the stomach?
Answer:
The stomach absorbs small amounts of water, alcohol, and certain drugs. Most nutrient absorption occurs in the small intestine.
Q45. What is assimilation?
Answer:
Assimilation is the utilization of absorbed nutrients by body cells for energy production, growth, repair, and maintenance of physiological activities.
Q46. Explain defecation.
Answer:
Defecation is the process of expelling faeces from the rectum through the anus. It is controlled by neural reflexes and voluntary muscle control.
Q47. What is diarrhoea and why is it dangerous?
Answer:
Diarrhoea is frequent passage of watery stools due to increased intestinal motility or infection. It is dangerous because it causes excessive loss of water and electrolytes, leading to dehydration.
Q48. What causes constipation?
Answer:
Constipation is caused by reduced intestinal motility, excessive absorption of water, low fiber intake, and inadequate hydration, leading to hard and dry stools.
Q49. Explain jaundice as a digestive disorder.
Answer:
Jaundice occurs due to malfunctioning of the liver, causing accumulation of bile pigments in blood. It results in yellowing of skin and eyes.
Q50. Why is absorption more efficient in the small intestine than in the large intestine?
Answer:
The small intestine has villi, microvilli, rich blood supply, and longer length, providing a large surface area for absorption. The large intestine mainly absorbs water and salts.